1. Field of the Invention
The present invention relates to a fuel injection valve for injecting fuel, and is applied to a fuel injection valve for injecting fuel which actuates a valve element from the valve closed position to the valve open position by an electromagnetic actuator.
2. Description of Related Art
A conventional type of fuel injection valve includes a valve seat formed in a valve casing, a downstream fuel adjusting passage for adjusting fuel quantity in the clearance between the valve seat and a contact portion which comes into contact with the valve seat, and an upstream fuel adjusting passage for adjusting the injection quantity in the same way as the downstream fuel adjusting passage on the upstream side of the downstream fuel adjusting passage (as disclosed in the Japanese Unexamined Patent Publication Nos. 2-163460 and 59-20562, etc.).
In such a conventional type of fuel injection valve as shown in FIG. 10, a valve element 73 formed in needle-like shape is slidably disposed in a guide space 72 in a valve casing 71. A valve seat 74 is formed in a conical surface at one end of valve casing 71, a contact portion 75 is formed so as to come into contact with the valve seat 74 at one end of the valve element, a downstream fuel adjusting passage 76 is formed between the valve seat 74 and the contact part 75, and an injection port 77 is formed at the bottom surface of the valve casing 71.
In the valve element 73, a sliding contact portion 78 is formed so as to be slidably disposed in the guide space 72 on the upstream side of the contact portion 75 (upper side in FIG. 10), and flat portions 79 are formed on the sliding contact portion 78 to form fuel flow passages. A projection portion 80 is formed on the upstream side of the sliding contact portion 78, and upstream fuel adjusting passages 81 are formed on the projection portion 80 so as to form throttles. Fuel is supplied into the fuel injection valve, then the fuel injection quantity is adjusted in the upstream fuel adjusting passages 81, then the fuel flows to the downstream fuel adjusting passage 76 through the flat portions 79, then the fuel injection quantity is adjusted again in the downstream fuel adjusting passage 76, and the fuel is finally injected from the injection port 77.
However, in such a conventional type of fuel injection valve as the above, it has been confirmed with experiments by the inventors of the present invention that the shape of the atomized fuel injected from the injection port 77 is not stable.
Namely, when fuel is supplied into the fuel injection valve, fuel flow F1 occurs as indicated with arrows in FIG. 11. At this time, the fuel flowing through the upstream fuel adjusting passages 81 generates whirls (i.e, eddies) around the flat portions 79 which have no throttle, and causes the fuel backflow from the downstream side of the flat portions 79 to the upstream side of the flat portions 79. The fuel flow F1 became instable due to the whirls, the atomization angle of the fuel injected from the injection port 77 varies in a range between .theta.1 and .theta.2, for example, as shown in FIG. 12. As a result, there is a problem that the fuel injection is not maintained in a constant condition. Furthermore, it is likely that such problem is easily caused by a small error in the shape of the upstream fuel adjusting passages 81. In practical use mounted on vehicles, etc., such a conventional type of fuel injection valve may cause emission deterioration or insufficient drivability.
On the other hand, another conventional type of fuel injection valve, which does not have the sliding contact portion 78 shown in FIG. 10, has the upstream fuel adjusting passage immediately above the downstream fuel adjusting passage (e.g., as in the Japanese Unexamined Patent Publication No. 59-20562). Even in this case, however, it has been confirmed that an error in the shape of the upstream fuel adjusting passages causes an uneven shape of the atomized fuel or injection failure.